The present invention relates to control valves, and more particularly to control valves and actuator devices for operation of the control valves. Even more particularly, the present invention relates to control valves and actuators for use in ultra pure applications.
The need for high purity chemical handling equipment is well established in the semiconductor industry. The degree to which a control valve, also referred to as a valve, is a high purity valve is measured by the contamination that it contributes to a gas or liquid stream that passes through the control valve. The difference in chemical content between what enters the valve and what leaves the valve is contamination, which may be either in a gas phase or fluid phase. There are essentially three sources of contamination associated with such valves.
First, the valve may leak atmospheric gas (e.g., air) into the liquid or gas stream (i.e., the material flow or the process flow), which is commonly referred to as an outboard leak. This is disadvantageous in that air, which contains about 1.5% moisture can contaminate the process flow. Typically, such outboard leaks occur due to actuation devices that allow the external environment access to the interior of the valve.
A second source of contamination is the valve may leak across a valve seat, which is commonly referred to as an inboard leak. This may lead to back streaming of other gases or fluids into a process gas or fluid or may lead to leakage of gas or fluid when it is not desired into a process, resulting in the presence of an otherwise desired chemical at the wrong time. Valves commonly leak across the valve seat due to a mis-alignment of a valve head-member and the valve seat or due to wear of the valve seat and the valve head-member or decomposition of particle matter on the valve seat.
A third source of contamination is the valve material itself may degrade and enter the gas or fluid stream. Valve components that are made of metal may degrade and contribute metallic contamination. Valve components made of elastomeric materials may degrade and contribute this as contamination. Such types of degradation may be further enhanced by the corrosive nature of the gas or liquid stream passing through the valve. Thus a high purity control valve is needed that minimizes these sources of contamination.
The present invention advantageously addresses the above and other needs.